The XA 13/18/21 mix of specific probes allows detecting copy number variations of chromosomes 13, 18, and 21. The green labeled probe hybridizes to a region at 13q14 including the RB1 locus, the blue (aqua) labeled probe hybridizes to a locus at 18q21, and the orange labeled probe hybridizes to a region at 21q22 including the DSCR4 (Down syndrome critical region 4).

Probe maps for selected products have been updated. These updates ensure a consistent presentation of all gaps larger than 10 kb including adjustments to markers, genes, and related elements. This update does not affect the device characteristics or product composition. Please refer to the list to find out which products now include updated probe maps.

Probe map details are based on UCSC Genome Browser GRCh37/hg19, with map components not to scale.

Numerical aberrations of autosomes 13, 18, 21, and sex chromosomes X and Y account for 95% of birth defects in newborns. FISH applied to uncultured amniocytes provides a method to identify those aberrations much faster than conventional chromosome analysis. It has become a standard to provide preliminary results for the detection of anomalies in less than 12 hours.

Duplications of chromosome bands 21q22.13-q22.2 have been shown to define the smallest region implicated in the causation of Down syndrome. Trisomy 13 syndrome is a rare chromosomal disorder in which all or a portion of chromosome 13 appears three times (trisomy). Based on molecular results, a region ranging from from 13q14-13qter has been found to be critically involved in Patau syndrome. Most of the features of Edwards syndrome have been shown to be associated with duplication of the region 18q12.3-q22.1. A locus-specific probe for 18q21 gives clearer signals and provides less ambiguous results compared to a centromeric probe for chromosome 18.

XA 13/18/21 hybridized to cultured amniocytes. A normal signal constellation is observed for 13q14 and 21q22, two green and two orange signals, respectively. For the 18q21 locus-specific probe three blue signals are shown.

• Bryndorf et al (1996) Am J Hum Genet 59:918-926
• Tepperberg et al (2001) Prenat Diagn 21:293-301
• Stumm et al (2006) Cytogenet Genome Res 114:296-301